Mixed lithography refers to lithographic processes involving more than one exposure source to create an image in a single layer of resist. See, for example, U.S. Pat. No. 8,334,090 issued to Fuller et al., entitled “Mixed lithography with dual resist and a single pattern transfer,” which involves use of an inorganic electron beam (e-beam) sensitive oxide layer which is exposed with an e-beam, and an ultraviolet sensitive photoresist layer which is exposed with an ultraviolet radiation. A mixed lithography approach allows one to take advantage of the lithography process best suited to produce particular features.
Hydrogen silsesquioxane (HSQ) is a material of interest for device fabrication since it can serve as both a low dielectric constant dielectric layer and as a resist material for high-resolution e-beam lithography. See, for example, S. Choi et al., “Comparative study of thermally cured and electron-beam-exposed hydrogen silsesquioxane resists,” J. Vac. Sci. Technol. B 26(5) (September/October 2008).
In the context of mixed lithography, for example, one might first deposit and pattern a dielectric using an optical lithography process, such as reactive ion etching (RIE). Next, HSQ is deposited and exposed using e-beam lithography. The different optical lithography and e-beam lithography exposures combine to create a common image in the sample. This process, however, involves multiple deposition, masking, and etching steps which increases the overall complexity and cost of manufacture.
Thus, improved mixed lithography techniques would be desirable.